Standalone photovoltaic DC energy systems must maintain bus voltage stability without grid support; however, abrupt load variations can cause a DC-bus voltage drop, reducing system reliability and disturbing connected equipment. Although battery-based energy storage is effective for long-duration power balancing, its response to instantaneous disturbances can be limited. This study proposes an energy stability strategy using supercapacitor-based ride-through control and required capacity sizing for fast DC-bus voltage support. The proposed controller continuously monitors the DC-bus voltage and, when a voltage drop is detected, immediately triggers supercapacitor discharge to compensate for the power deficit until the bus recovers. In addition, a design formulation is derived to estimate the required compensation energy, ride-through time, and minimum capacitance based on the expected power deficit, allowable DC-bus voltage drop, and initial supercapacitor voltage. Simulation results under step changes in load resistance show that the supercapacitor sized by the proposed method maintains the DC-bus voltage close to its reference value within the specified limit. Hardware experiments further validate the ride-through operation and show good agreement between the predicted and measured compensation times.
Won et al. (Tue,) studied this question.